The present invention relates to a control system for a multi-stage reducing apparatus through which elongate material is advanced and reduced in cross section. The invention is particularly suitable for use in connection with apparatus, e.g., metal strip rolling mills and wire drawing machinery, having a series of material reducing stages through which elongate material is continuously advanced and progressively reduced in cross sectional area.
It is known in the prior art to reduce the cross section of elongate metal material by advancing the material through successive stages of multi-stage reducing apparatus. Each stage includes a material advancing mechanism and an opening of smaller size than the cross section of the material advanced to the stage. The openings at successive stages of the apparatus are progressively smaller in size so that the cross section of the material is progressively reduced as the material is advanced. When the material leaves the opening of the final material reducing stage, it has the desired cross sectional shape and size. Multi-stage rolling mills and multi-stage wire drawing machines represent examples of this general type of equipment.
As a result of the reduction in cross sectional area of the material at each opening, the material experiences an elongation in passing through each opening. Consequently, it is necessary for the material advancing mechanisms at the successive stages of the reducing apparatus to operate at progressively increasing speeds from the initial to the final stage.
When operation of such multi-stage reducing apparatus is initiated from rest, it is necessary for the prime movers, e.g., electric drive motors, of the material advancing mechanisms to be operated at desired fixed relative speeds during the acceleration period to avoid possible breakage or the production of excessive material between the material reducing stages. The same fixed proportional relationship of material speeds at the various stages is required in the operation at normal running speed for the same reasons. Consequently, it is essential for successful operation of such multi-stage reducing apparatus to provide precise regulation of the speed of the material at each of the material reducing stages.
Control arrangements for multi-stage reducing apparatus have been previously proposed to allow an operator to preset the desired ratio of speeds between the material advancing mechanisms of the reducing stages. An example of one such arrangement is described in U.S. Pat. No. 3,688,546, issued on Sept. 5, 1972 to Jean Tranier. This patent discloses a speed control arrangement for a multi-stand reducing apparatus in which a dial or rule associated with each stand is provided with a logarithmic scale for representing the size, i.e., diameter, of the material at each stand. The dials are coupled together to provide equal movement of all dials simultaneously. The logarithmic scales on the dials are progressively offset relative to the dial associated with the final stage, with the progressive offset between the dials corresponding on a logarithmic scale to the base speed ratios between the material reducing stands. The machine operator must visually align the logarithmic scales on the dials with a series of hairlines to obtain desired size settings. A general speed signal is applied across a parallel array of voltage dividers, one for each stand, with a pickup for each divider arranged to supply its associated drive motor with a speed control voltage dependent on the general speed control signal and the position of the pickoff along its divider. Each pickoff, other than the final or finisher stand, is adjustable through a limited range to provide an approximately linear relationship between voltage changes and the logarithmic scale.
Because of the necessity for an operator to manipulate the dials relative to visual hairlines, it is difficult to obtain accurate material size settings on such a control mechanism. Since all dials are coupled together for simultaneous movement, the control arrangement does not permit any flexibility in the section of relative material size settings at the various stands. In addition, because of the limited range of adjustment of the voltage dividers required to preserve the necessary linear relationship between the voltage changes and logarithmic scale, the range of material size settings is restricted.
A primary objective of the present invention is to provide an improved system for controlling a multi-stage reducing apparatus to achieve more precise speed control of the material at the material reducing stages. Another object of the invention is to provide a control system for a multi-stage reducing apparatus which is conveniently and accurately operable over a wide range of material sizes. It is also a purpose of the invention to achieve a multi-stage reducing apparatus in which the material speed at each of the reducing stages is accurately controlled according to the material speed at a predetermined stage and the ratio of the cross sectional areas of the material at the predetermined stage and the particular stage.
In accordance with the present invention, a control system for a multi-stage reducing apparatus having a series of material reducing stages through which elongate material is continuously advanced and progressively reduced in cross section comprises means for generating a set of signals representing the cross sections of the material at each of the stages, means for generating a speed control signal representative of the speed of the material at one stage, and control means responsive to the cross section signals and the speed control signal and operable for producing a plurality of speed reference signals for controlling the speed of the material at each stage, each such reference signal being proportional to the speed control signal and the ratio of the cross section of the material at said one stage and the cross section of the material at the respective stage. The control means is preferably embodied as a plurality of analog arithmetic units, for the plurality of stages, each responsive to the speed control signal and to the cross section signals of said one stage and the respective stage and operable for generating an output signal corresponding to the product of the speed control signal and the ratio of the cross sections of the material.
A preferred embodiment of the invention may be embodied as a multi-stage wire drawing apparatus for advancing and drawing continuous wire material stock and comprising a series of material drawing stages each including a rotatable draw block for advancing the wire material stock, a drive motor for rotating the draw block to advance the wire material stock and a die having an opening for reducing the cross sectional area of the wire stock.
It will be understood that the term "opening" used herein encompasses both the spacing between rolls in a metal strip rolling mill and the bore in a die of a wire drawing machine. However, the term "opening" is not intended to limit the scope of the present invention to only those types of reducing machines. In addition, the preferred embodiment may include a gear train at each stage for connecting its drive motor to its respective rotatable block, and means for modifying the speed reference signals to compensate for the different gear ratios.
The present invention also contemplates a method of controlling a multi-stage reducing apparatus having a series of material reducing stages through which elongate material is continuously advanced and progressively reduced in cross section and wherein each stage has a drive unit for advancing the material at a speed determined by an applied signal. The method comprises generating a first signal representing the cross section of the material at one of the stages, generating a set of second signals representing the cross sections of the material at each of the other stages, applying a speed signal to the drive unit at the one stage to control the speed of the material at that stage, combining the first signal with each of the second signals and with the speed signal to produce a plurality of reference signals proportional to the speed signal and the respective ratios of the cross section of the material at the one stage to the cross sections of the material at each of the other stages, and applying the reference signals to the other drive units to control the speed of the material at each of the other stages.
The present invention achieves a system and method of controlling the operation of a multi-stage reducing apparatus in which the speed of the material at each reducing stage is precisely controlled. In addition, the invention is readily adaptable to control a multi-stage reducing apparatus over a wide range of material size.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
A better understanding of this invention will be obtained from the following detailed description and the accompanying drawings of an illustrative application of the invention.